1. Field of the Invention
The present invention relates to a copper alloy conductor (a trolley wire) for electric train lines, which is formed of a high-conductivity and high-strength copper alloy material and which supplies power to electric trains via pantographs, etc., a cable conductor for equipment used in cables for equipment of each kind, and an industrial cable conductor used for general industrial cables (heat-resistant electric wires, cables for robots, cab tire cables).
2. Description of the Related Art
In copper alloy conductors (trolley wires) for electric train lines, or in cable conductors for equipment used in cables for equipment of each kind, there are used high-conductivity hard copper wires, or abrasion-resistant and heat-resistant copper alloy materials (copper alloy wires). Copper alloy materials are known that contain 0.25 to 0.35 wt % of Sn in copper parent materials (See JP-A-57-140234), and they are used as trolley wires for Shinkansen lines (or bullet train) and conventional railway lines, and cable conductors for equipment.
In recent years, there has been progress in higher-speed trains. Increasing the train speed requires enhancement in the tension of overhead wires, so that the tension of overhead wires in train lines tends to be increased from 1.5 t to 2.0 t or higher. Also, in train lines with high passing train density (the number of passing trains per unit line length), there is a demand for larger current capacity of trolley wires.
Also, in cable conductors for equipment, taking account of use environments, there is a demand for better bend-resistant, i.e., higher-strength conductors. In cable conductors for equipment, to meet needs for lighter weight and smaller size, there is also a demand for higher conductivity.
Further, in industrial cable conductors, there is also a demand for conductors that inhibit reductions in conductivity as much as possible, enhance strength and heat resistance, and has good bend resistance, taking account of use environments.
Accordingly, as conductors that meet these demands, high-strength and high-conductivity copper alloy conductors are needed.
As high-strength copper alloy conductors, there are mainly 2 kinds: solid solution-strengthening alloys and precipitation-strengthening alloys. As solid solution-strengthening alloys, there are Cu—Ag alloys (high-concentration silver), Cu—Sn alloys, Cu—Sn—In alloys, Cu—Mg alloys, Cu—Sn—Mg alloys, etc. Also, as precipitation-strengthening alloys, there are Cu—Zr alloys, Cu—Cr alloys, Cu—Cr—Zr alloys, etc.
Any of solid solution-strengthening alloys has an oxygen content of 10 wt·ppm (=0.001 wt %) or less, and are excellent in strength and elongation properties, which allows copper alloy wire rods that serve as parent materials of trolley wires to be made directly from melted copper alloys by continuous casting and rolling.
As a fabrication method of conventional trolley wires using solid solution-strengthening alloys, a copper-alloy cast material containing 0.4 to 0.7 wt % of Sn, for example, is hot-rolled at temperatures of 700° C. or more. This rolled material is again heated at temperatures of 500° C. or less, followed by finishing rolling to form a wire rod, from which the wire is drawn to make a trolley wire (See JP-A-6-240426).
Also, as other copper alloys that can be continuously cast and rolled, there are Cu—O—Sn alloys. It is known that these Cu—O—Sn alloys have a crystallized substance (SnO2) with Sn of a 2-3 μm size or more present inside a matrix, and that their strength and elongation properties are equal to those of Cu—Sn alloys, the oxygen content of which is 10 wt·ppm or less. These alloys also have the stronger solid solution-strengthening effect than the precipitation-strengthening effect and dispersion-strengthening effect.
In solid solution-strengthening alloys, the enhancement of strength can be ensured by increasing its solid solution-strengthening element content. However, because it substantially reduces conductivity, electric current capacity cannot be large, which would result in no suitable electric train lines. For instance, a fabrication method described in JP-A-6-240426 results in a low conductivity because the Sn content is as large as 0.4 to 0.7 wt %. Thus, in conventional Cu—Sn-based alloys, there is difficulty in making copper alloy conductors that have strength required for high-tension overhead wires, and good conductivity.
Here, to obtain high-strength and high-tension electric train lines, another element together with Sn is considered to be further added. In this case, there is the problem that too low finishing rolling (final rolling) temperatures would cause many cracks in a rolled material during rolling, so that the quality of wire rod appearance and electric train line strength would degrade substantially.
On the other hand, although precipitation-strengthening alloys have very high hardness and tensile strength, high hardness would cause an excessive load to mill rolls during continuous casting and rolling, which would make fabrication by the continuous casting and rolling impossible. For this reason, precipitation-strengthening alloys can be produced only by batch methods such as extrusion, etc. In addition, precipitation-strengthening alloys require thermal treatment for precipitation of precipitatibn-strengthening substances in an intermediate step. Thus there is the problem that precipitation-strengthening alloys are low in productivity and high in manufacturing cost, compared with solid solution-strengthening alloys that can be made by continuous casting and rolling.
That is, there are constraints and limits in manufacturing high-strength and high-conductivity copper alloy conductors using a continuous casting and rolling method that is excellent in productivity.